The present invention relates to the magnetic recording media such as video-tapes, audiotapes and others, and particularly to the improvement of the performance of the magnetic recording media such as running stability, still life and others.
Generally, the magnetic recording media are manufactured through the method wherein magnetic coatings containing a magnetic powder, a binder and others are coated on a support and then dried, Recently, the development of the magnetic recording media has requested a high-grade tape performance for the magnetic tapes for the use of video, computer, audio and others. A still life and a stable running property are especially required for the video-tape whose relative speed is high. Therefore, it is very important to reduce the running friction of the tape as well as the abrasion resistance of the tape itself.
For the purpose of reducing the friction of the magnetic layer, adding of various types of lubricants (i.e. silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid and fatty acid ester consisting of monohydric alcohol having 21.about.23 carbon atoms that represent a total of monobasic fatty acid having 12.about.16 carbon atoms and the number of carbon atoms of the fatty acid) has hitherto been known. Despite an addition of foregoing lubricants, however, no satisfactory charcteristics have so far been obtained and it has been impossible to avoid undesirable phenomena such as blooming and other, in particular.
Head-clogging or head-deterioration has hitherto been prevented by the so-called head cleaning action wherein a magnetic layer is reinforced by the use of fine powder abrasives and moderate roughness is given to the surfaces of the magnetic layer and thereby foreign materials piled up on the head are removed.
For example, Japanese Paten Examined Publication No. 39402/1974 discloses that the combination of a fatty acid having the melting point (hereinafter referred to as mp) of 50.degree. C. and below and the abrasives having the particle size of 5 .mu.m and less and the Mohs' hardness of 6 and over improves the still life remarkably compared with the case wherein neither fatty acid nor abrasives are contained.
As observed in Japanese Patent Examined Publication No. 39081/1976 and Japanese Patent Publication Open to Public lnspection No. 130435/1983, on the other hand, there have been suggested the technologies to cause fatty acid ester having an RCO group with the number of carbon atoms of from 10 to 16 and a fatty acid having the mp of from 44.degree. to 70.degree. C. to be contained in the magnetic layer. The combined use of these fatty acid ester and a fatty acid is considered to prevent the aforesaid phenomena. Namely, although it is generally known that fatty acid ester itself reduces the friction by reducing surface free energy, if the mp of the fatty acid ester is 20.degree. C. and below, the blooming takes place at room temperature and on the occasion especially of tne storage under high temperature and high humidity and the stickiness is produced, thereby the running property is deteriorated.
Further, the mixture ratio of fatty acids and fatty acid ester both have hitherto been used for lubricants and the amount thereof have been adjusted so that they accord with magnetic materials in the iron oxide group. Therefore, when the surface properties like the metal powder that differ from the oxide powder are owned, the desirable performance has not yet been achieved and the conventional ratio of acid and ester has caused the running property to be unstable.